The following relates generally to electrically controlled valves which can operate in a strong magnetic field. It finds particular application in conjunction with low-pressure fluid valves which operate near a magnetic resonance imaging scanner, and will be described with particular reference thereto. However, it will be understood that it also finds application in other usage scenarios and is not necessarily limited to the aforementioned application.
Electrically controlled valves with solenoids or ferrous parts are adversely affected near strong magnetic fields such as in a magnetic resonance (MR) room or in the bore of an MRI scanner. Valves which operate in a strong magnetic field include non-magnetic materials or are designed such that the magnetic materials are removed or shielded from the magnetic field. The presence of magnetic materials can affect operation of the valve device and can potentially act as projectiles. Valves are used for controlling fluids such as anesthesia gas supply during magnetic resonance guided surgery, air pressure control in non-invasive blood pressure (NIBP) monitoring, oxygen supply for patient life support, measuring patient gas expiration, and the like. One acute area of need includes neonatal applications where volumes of gas are small and close adjustment of fluid flow is important.
One approach is to use a valve switched pneumatically from a traditional valve location outside the magnetic field, e.g. located outside a shielded room with pneumatic connections. The disadvantage is the use of a compressed air supply, bulky pneumatic tubing, and noise. Another approach is the use of shielding to shield ferrous valve parts from external magnetic fields. However, shielding makes use of ferrous materials such as iron which make the shielding subject to distorting the magnetic field and becoming potentially projectiles.
Valves typically include a spring or biasing element which biases the valve by default either open or closed. Springs materials subject to the strong magnetic fields, and in some instances, can collapse under the magnetic forces. Alternatively, springs can be made from non-magnetic materials such as beryllium-copper or phosphor-bronze but the material is costly. Furthermore, the non-magnetic materials can be found to change their spring constant over time which makes them less reliable in medical care applications.
Another approach is the use of valve materials which are not subject to the magnetic field. For example, piezoelectric diaphragm valves are used, but are typically physically large and need very high drive voltages. The diaphragm includes a covering of piezoelectric material which operates to change shape and directly open or close a valve port when an electrical charge is applied. The high voltage drivers are expensive and difficult to implement in magnetic field because they often have components which are also subject the magnetic field. Another example includes piezoelectric bending actuators such as a flap which bends to directly open or close a valve. Both examples include a spring element or biasing element which is subject to wear and difficult to replace and/or repair. Both examples include a valve which operates in analog manner between the valve being either completely open or completely closed.
The following discloses a new and improved linear digital proportional piezoelectric valve which addresses the above referenced issues, and others.